1. Field of the Invention:
This invention relates to a processing method of binary-coded image data which represent a mask in terms of binary-coded data, and especially to a method for smoothing mask boundaries by converting picture element data of a low resolution into their corresponding high resolution data and an apparatus suitable for use in the practice of the method.
2. Description of the Prior Art:
When binary-coded image data are output and then displayed or recorded, a stair-like zig-zag boundary appears as shown in FIG. 11(a) where the boundary between logical values "1" and logical values "0" is oblique. In FIG. 11(a), each piece of the picture element data is shown by a single piece of square and the squares of logical value "0" are shown as plain squares and the squares of logical value "1" are indicated by hatchings. A variety of methods have heretofore been proposed to make such zig-zag boundaries less noticeable.
As one of such prior art proposals, picture element data are divided and the thus-divided picture elements are again binary-coded in accordance with their respective peripheral picture data to smoothen the boundary as illustrated in FIG. 11(b). This method is disclosed for example in Japanese Patent Publication No. 30573/1983. It may also be contemplated to perform further division of the above-divided picture element data as shown in FIG. 11(c).
The above patent publication, it is disclosed to employ an ROM, to which pattern data on peripheral picture elements are input, so as to obtain data on divided picture elements. However, it neither discloses nor suggests anything how to prepare the data on the divided picture elements for their writing in the ROM.
It appears that as is routinely practiced, the patterns of the peripheral picture elements are empirically classified into groups and data patterns of the divided picture elements are manually determined one by one in accordance with the thus-classified patterns of the peripheral picture elements.
When picture elements which are to be processed are divided into 3.times.3 or 5.times.5 in accordance with the peripheral picture elements of 3.times.3 pieces as depicted in FIGS. 11(b) or 11(c), 512 data patterns can be contemplated for the resulting divided picture elements. These data patterns may still be manually determined with ease.
However, the above-mentioned manual approach is practically impossible to perform smoothening while taking the peripheral picture elements of a broader region into consideration so as to improve the smoothness of the resultant picture quality. If one wants to make an improvement in resolution, for example, to peripheral picture elements of 5.times.5 pieces (namely, the picture element which is to be processed is divided into 5.times.5 pieces), such a huge number of data patterns as many as 2.sup.25 (=33,554,432) are required for the divided picture elements.
For the single piece of central data pattern of the peripheral picture elements of 5.times.5 pieces, it is indispensable to use divided picture element data of 2.sup.25 .times.5.times.5 pieces in total when the central data pattern is displayed in 5.times.5 pieces. If one tries to carry out the above processing by means of an ROM, about 3,200 memory chips of 256 kilobits each are required. This is certainly impractical from the economical standpoint too.